Many educators are introducing meditation into the classroom as a means of improving kids’ attention and emotional regulation. A five-minute walk from the rickety, raised track that carries the 5 train through the Bronx, the English teacher Argos Gonzalez balanced a rounded metal bowl on an outstretched palm. His class—a mix of black and Hispanic students in their late teens, most of whom live in one of the poorest districts in New York City—by now…